1. Field of the Invention
The present invention relates to a key-less entry system for remotely controlling vehicle door locks by using a transmitter.
2. Prior Art
Key-less entry systems for remotely controlling vehicle doors from a distance by using a transmitter are in widespread use today because of their convenient functions. However, when a user wants to lock the vehicle doors after unloading, from the vehicle, an amount of goods that he must carry with both hands, the user has to first place the unloaded goods on the ground and then operate the transmitter to lock the doors, and this causes great inconvenience to the user. One possible solution to this would be to automatically activate the door locks a predetermined time after the closure of the last door even when a lock signal is not transmitted, but this could cause inconvenience because the doors are automatically locked, by just closing the last door, when the user has no intention of locking the doors.
To avoid such a situation, the system disclosed in Japanese Unexamined Patent Publication No. 9-217534 is configured so that automatic locking will be permitted when an unlock request is transmitted using a transmitter after the doors are closed. However, in the system disclosed in Japanese Unexamined Patent Publication No. 9-217534, as the transmitter has to be operated once again to perform the automatic lock after the doors are closed, the earlier described problem cannot be solved, that is, when the user's hands are occupied, the user has to first place the goods on the ground and then operate the transmitter. Prior art examples of automatic lock functions include those employed in the systems disclosed in Japanese Unexamined Patent Publication Nos. 5-156851 and 10-196181. In the former system, a portable transmitter and a receiver each incorporate a transmitting/receiving circuit, and a weak search signal is transmitted at periodic intervals from the receiver, with provisions made to lock the doors unless the portable transmitter receives this search signal and returns an ID code to the receiver. According to this prior art system, when the user carrying the portable transmitter moves away from the vehicle, the portable transmitter goes out of the range of the search signal being transmitted from the receiver, and hence, does not return the ID code; in this way, the doors can be locked automatically without operating the transmitter. However, the disadvantage with this system is that the configuration becomes complex and the cost increases because both the portable transmitter and the receiver have to be equipped with a transmitting/receiving circuit.
On the other hand, the system disclosed in Japanese Unexamined Patent Publication No. 10-196181 solves the problem of the system disclosed in Japanese Unexamined Patent Publication No. 5-156851 by making provisions to normally lock the doors upon reception of a lock request from the transmitter and to switch to an automatic lock mode only when prescribed conditions are satisfied. According to this prior art system, neither the portable transmitter nor the receiver need be provided with a transmitting/receiving circuit, and an automatic lock function reflecting the intention of the user can be achieved with simple configuration. However, the system disclosed in Japanese Unexamined Patent Publication No. 10-196181 requires extremely complicated conditions to activate the automatic lock mode. That is, in this system, the automatic lock mode is activated only when all the prescribed conditions are satisfied, including the condition (1) that the driver enters the vehicle and drives the vehicle and the condition (2) that the unlock switch on the transmitter is operated twice after finishing the driving of the vehicle. Accordingly, it is not easy to activate the automatic lock mode, and the drawback is, for example, the user cannot switch the mode to the automatic lock mode, when the user so desires, without starting the vehicle.